And a lot of water is going to come out of the reservoir in the process of their investigation.

Bureau of Reclamation officials said Friday that about 10 feet of water will have to be taken out of Willard Bay in order to inspect the dam and locate the sources of seepage. That translates into about 100,000 acre-feet - or more than half the water that was in the reservoir that serves the Ogden area when the leaking first occurred.

"It's a lot of water," Bureau of Reclamation spokesman Barry Wirth said. "The problem is, we have to get down to where we can examine the face of the dam and the reservoir base. Unfortunately, that means taking water out, and we need to do it sooner rather than later."

To expedite the process, Wirth said the bureau is bringing in pumps from New Mexico that are scheduled to arrive this weekend. Water is currently being released through an outlet into the Great Salt Lake.

Water seeping out of the Arthur V. Watkins Dam was initially discovered a week ago and reported to the Bureau of Reclamation and Weber Basin Water Conservancy District last Monday. Initial repairs were completed that night. Since then, engineers have been working to discover the cause of the seepage, which eroded a portion of the earthen dam.

As the reservoir is lowered, crews will also begin placing sand and gravel materials into the upstream side over the suspected seepage entrance points, which will seal them.

Willard Bay was at about 80 percent capacity before the leak was discovered, holding about 175,000 acre-feet of water.

The planned draw-down will leave enough water to protect Willard Bay's existing fishery. Fishing had earlier been closed for the season. In the wake of the dam seepage, boating is also now prohibited.

Wirth says it is still unknown to what extent the water supply will be impacted by the repair project. But for now, the priority has to be on ensuring the dam is secure.

"The district can't run the facility until it's safe, and it won't be safe until we do what we have to do," said Wirth. "We want to get the work completed as soon as possible so the reservoir can refill it in the spring."

jbaird@sltrib.com